MAQ Magazine n. 10 / February 2019
Astronomers using ESA’s galaxy-mapping spacecraft Gaia have discovered the first direct evidence that white dwarfs form crystal cores of metallic oxygen and carbon. This process of crystallization was predicted five decades ago but it wasn’t until the arrival of Gaia that scientists were able to observe enough of these objects with such a precision to see the pattern revealing the process.
White dwarfs are the remains of medium-sized stars similar to our Sun. Once these stars have burnt all the nuclear fuel in their core, they shed their outer layers, leaving behind a hot core that starts cooling down.
Image above right: an artist’s impression of some possible evolutionary pathways for stars of different initial masses. Some proto-stars, brown dwarfs, never actually get hot enough to ignite into fully-fledged stars, and simply cool off and fade away. Red dwarfs, the most common type of star, keep burning until they have transformed all their hydrogen into helium, turning into a white dwarf. Sun-like stars swell into red giants before puffing away their outer shells into colorful nebula while their cores collapse into a white dwarf. The most massive stars collapse abruptly once they have burned through their fuel, triggering a supernova explosion or gamma-ray burst, and leaving behind a neutron star or black hole. Image credit: ESA.
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